The problem with taking away stats and replacing all the stat-related racial bonuses with mutations (Or whatever you want to call the new thing that replaces those bonuses) is that suddenly you have to maintain a whole additional set stat-mimicing mutations, and if they use the existing mutation mechanic, they have less granularity than stats do. If they *don't* use the existing mutation mechanic, then you have to add a whole different mechanic, which replaces stats, which doesn't simplify anything at all.
The alternative is to simply not have races be distinguished by things like "this race is better at spells than that race, even training everything to max" if there wasn't a cap to skills, aptitude would be an acceptable distinction, but there is, so it's not. (Yes, I suppose races could have different skill caps, good luck on getting that level of structural change implemented
If you take away the distinction entirely, then you have less possible racial variation, and therefore less races, and thereby less replayability, (Which isn't horrible, but honestly this strikes me as a solution looking for a problem) Yes simplification of the game where complication adds nothing is a good thing, however in this case having stats gives us an axis around which we can build distinction between characters, and god(s) (I guess chei could come up with an entirely new mechanic, or simply be retired) and between artifacts, (but honestly artifacts are already pretty distinctive, they could probably withstand the loss of stat boosting without too much 'samey-ness' being introduced) If you remove the axis you can either replace it, or reduce your distinctiveness.
To simplify it while replacing it and retaining the level of variation it gives, you'd have to come up with a system that is simpler than a *single number*, you could reduce the variation to simplify it, but this is the same as retaining stats and just increasing their granularity; If there's a "is better/worse with spells" mutation to replace int using the current mutation mechanic , then that's exactly the same as reducing Int to a scale of 7 (-3 through +3) from it's current scale.
At that point the argument is "Stats shouldn't be shown in the on screen display area" which is a different argument altogether.